The basic idea behind the invention comes from the agricultural sector where disadvantages have been found by the existing methods for weight determination of individuals on different stages of the growth period.
Subsequently, in the period of development, other areas of application have been found, as e.g. the health sector, where there are drawbacks by the existing methods for water content determination of individuals on different stages of a period of sickness.
In the agricultural sector, it is important for the farmers raising animals for slaughter to get the greatest possible growth rate from the amount of feed used simultaneously with providing for the environment by e.g. reducing the discharge of nitrogen.
Experience shows that the optimal feeding of the single animal for growing as fast as possible without achieving an undesirable large fat percentage is to provide it with feed with a content of energy and protein suitable for the growth stage of the animal during the growth period.
The feed may e.g. contain different amounts of grain, proteins, vitamins, minerals and/or drugs.
It will be optimal that the farmer keeps a close eye on the weight of the animal, so that the ratio between the feed grade/protein level, and the growth of the animal is registered whereby the composition and feed amount may be adjusted.
In order to achieve maximum optimisation in growth of an animal in its entire growth period, it is necessary that the animal is weighed at least once a day, and that this measurement is compared with the dispensed amount of feed and feed grade and protein level.
For weighing loose animals, there are used types of weighing apparatuses that are typically designed with a plate on weigh cells and a cage for keeping the animal on the plate during weighing.
A number of weighing systems are described in patent publications as WO 01/17340, WO 98/47351, U.S. Pat. No. 5,579,719 and GB 2,220,834 that may identify an animal walking on a weight and where the result is used for special feeding of single individuals.
The problem with the above types of weights is that they are very expensive and the weight installation requires some space and some maintenance as they are continually placed in an aggressive stable environment.
There is described an apparatus in DE-A1-44 32 849 where the mass of an item may be determined. The drawback of this apparatus is that its system of a measuring cell and a coil in a oscillatory circuit cannot be used for measuring conducting items, as e.g. living individuals, as the oscillator of the apparatus will stop oscillating if an electric conducting item passes the measuring cell.
In the health sector it is important to register the water content of a patient for e.g. diagnosis at dehydration of the patient or by accumulation of water in the patient's body, so that a real treatment of the patient may be performed.
Today, diagnosis occurs on the basis of the symptoms displayed by the patient, which is at a time where the patient has advanced into the period of sickness.
Therefore, it would be optimal if it was possible at an early time in the period of sickness to perform a sure diagnosis forming basis of a treatment, and subsequently check this diagnosis at regular time intervals by means of a registration apparatus.
DE-A1-44 46 346 describes an apparatus, which makes it possible to measure the change in body part electrolyte volume, which body part is positioned between two capacitor plates.
The disadvantage of the apparatus according to DE-A1-44 46 346 is that the measurement of the electrolyte volume change only concerns the body part volume and not the body part weight.
According to DE-A1-44 46 346 the resonant frequency is preferably described in MHz range. This is, however, a disadvantage as frequencies in MHz range causes the capacitor plates to act as an antenna, and it is impossible to measure any electrolyte volume change.
Furthermore, high resonant frequency demands smaller capacitor plates and a small distance between the capacitor plates for functioning. This only allows measurement of a small electrolyte volume; hence the apparatus does not apply to large body parts or entire animals, e.g. pigs.
From looking at FIGS. 2 and 3 and the complying description one derives that the electrical circuits shown are either oscillating circuits or simple measuring bridges. The oscillating circuit does not function properly as no frequency variation occur due to the use of only one resistor and one capacitor in the circuit, thus the oscillating circuit only acts as a non-oscillating filter. The simple measuring bridge only measures change in electrolyte volume
According to EP-A2-1 091 215 a bioelectric impedance measuring apparatus for humans is described having a number of electrodes. Measurement is only performed, when a barefooted person is positioned on the electrodes, hence being in galvanic contact with the electrodes, as current is sent through the electrodes into the person's body and the impedance is measured and the data is computed into different body constitutions.
It is not possible to imagine an animal standing accurately enough for current to be sent through the feet/legs in order to measure impedance. Furthermore, the apparatus does not measure accurately, when a hoofed animal is positioned on the electrodes, as the hooves function as an electrical isolator. Another disadvantage is that the hooves of any animal, e.g. pig hooves, are dirty and the dirt intervenes with the impedance measurement.
It does not appear from EP-A2-1 091 215 that two sets of electrodes can be arranged opposite each other, instead it appears that the person is in galvanic contact with both sets of electrodes, which allows the apparatus to measure the conductivity and compute the person's weight.